The present invention relates to a process and apparatus for uniformly cooking materials, and the products formed thereby and, more particularly, relates to a multi-fluid spray nozzle apparatus and process for atomizing a material, such as a suitable starch, and for simultaneously cooking that material. Preferably, a material capable of gelatinization, such as a starch, is uniformly gelatinized by the process and by use of the apparatus of this invention.
The present invention is particularly applicable to the atomization and cooking or gelatinization of materials which are normally difficult to cook or gelatinize and spray dry due to the generation of high viscosities in the materials during cooking or gelatinization.
For many materials, such as starches, it is desirable to perform various chemical or physical modifications of the material when the material is in the form of a slurry, followed by drying the slurry by, for example, spray drying. When a starch, such as corn starch is in an ungelatinized (uncooked) state, then spray drying the resultant slurry is generally straight forward and may be carried out using conventional atomizers. However, when the starch is in a gelatinized (cooked) state, then spray drying the resultant slurry becomes more difficult and complex due to the increased viscosity of the starch slurry and the shearing to which the gelatinized starch granules are subjected to during atomization and spray drying. Gelatinization occurs when an aqueous starch slurry is heated beyond a critical temperature (e.g., above about 65.degree. C. for corn starch), the starch granules absorbing water and swelling resulting in a slurry with increased viscosities. For example, a slurry with 10% by weight of gelatinized corn starch generally has a viscosity of about 600 centipoises and a slurry with 15% by weight of gelatinized corn starch generally has a viscosity of about 20,000 centipoises, while a slurry with similar amounts of ungelatinized corn starch will have a viscosity similar to water (i.e., about 1 centipoise). When a gelatinized starch slurry having such high viscosities exits the cooker, then drying the starch by use of a rotary atomizer or spray nozzle in a spray dryer is unsuitable. Not only would the gelatinized starch slurry be difficult to pump and atomize due to the high viscosities generated, but the swollen starch granules would be subject to substantial shearing action during atomization and pumping which would destroy the granule integrity of the starch. Thus, while prior art processes have pumped, atomized and spray dried slurries having up to 10% by weight of gelatinized starch, slurries of about 15% by weight or greater of gelatinized starch could not be effectively pumped, atomized or spray dried by conventional techniques while maintaining whole granule integrity.
Several types of two- and three-fluid nozzles are currently commercially available. With these nozzles, air is commonly used in the atomization process, and steam is occasionally mentioned as being an appropriate fluid for heating (not cooking) and conveying a material. Nozzles and processes of this type which are in common use or disclosed in the prior art literature may be readily found in the following United States patents:
______________________________________ Patentee U.S. Pat. No. ______________________________________ Higgins 1,450,631 Hickey 3,342,607 Knoch 3,374,096 Simmons, et al 3,474,970 Dindell, et al 3,628,734 Meyer, et al 3,674,555 Duren 3,689,288 Helmrich 3,684,186 Strommer 3,730,729 Tamai 3,887,135 Hildebolt 4,039,691 ______________________________________
However, none of these patents disclose or suggest the inventive process or multi-fluid nozzle apparatus for uniformly cooking or gelatinizing materials as described herein.